1. Field of the Invention
The present invention relates to a bearing which seals a space between an outer ring and an inner ring, and a developing apparatus using the bearing.
2. Description of the Related Art
Conventionally, a bearing has been known as a shaft supporting means holding a rotating shaft. This bearing smoothly rotates an inner ring 201 by a configuration, as shown in, for example, FIG. 9, in which a plurality of balls 203 held with a retainer 202 at a predetermined interval are interposed between an outer ring 200 and an inner ring 201.
However, rolling of the balls is obstructed by dirt which enters into spaces formed by the outer ring 200, the inner ring 201, and a ball 203 because the spaces are made as small as possible in order to remove looseness.
Then, there are some cases in which a sealing member 204 is mounted on the side surface of the outer ring 200 and the inner ring 201 in order to prevent damages to grooves on the rings and the ball 203. Generally, this sealing member 204 is configured not to easily be detached, based on a configuration in which the sealing member 204 is formed of doughnut-shaped thin sheet metal, and the outer diameter portion of the metal 204 engages with a groove 200a provided on the outer ring 200, using the spring characteristics.
Moreover, grease can be filled into the bearing as a lubricant in the case of a metal bearing. Thereby, the mechanically contacting portions of the bearing can be lubricated with the grease to improve the durability of the bearing.
Here, when a sealed bearing is formed of plastic, a material, which is provided with resistance to chemical attack and the like by lubricating grease filled in the bearing and has high wear resistance, is required to be worked with high accuracy. Recently, a high-performance material has been developed and provided, especially, in a field of engineering plastic. Thereby, a bearing made of plastic has been developed (Japanese Patent Application Laid-Open No. 9-273546).
The above-described bearing has been widely used for an image forming apparatus. For example, a spacer roller is disposed between a developing apparatus and a photosensitive drum, and some of the spacer rollers are obtained by specially fitting plastic to the surroundings of an outer ring in a metallic bearing (Japanese Patent Application Laid-Open No. 6-175481).
An electrophotographic type image forming apparatus forms an image, using toner. Because the toner is fine powder, the toner is dispersed and easily enters into a bearing to have a possibility that rolling of the ball is obstructed. Recently, the particle size of the toner for an electrophotographic type image forming apparatus has become finer and finer as digitization and colorization proceed. Thereby, bearings used for the above-described image forming apparatus have been required to have excellent sealing properties.
However, there has been a problem that higher costs and more complex structures are required because a higher working accuracy is required in the case of a metal sealed bearing. Moreover, there is absolutely caused a space in the case of sealing between metals to invite a possibility that fine toner powder enters into the space even through a minute gap.
Moreover, in the bearing made of plastic shown in Japanese Patent Application Laid-Open No. 9-273546, an auxiliary ring different from the outer ring and the inner ring is prepared, and the auxiliary ring is fitted to between the side surfaces of the outer ring and the inner ring as a sealing member. As a process for fitting the sealing member has been required as described above, and there is a gap between the auxiliary ring and the inner ring, complete sealing has been difficult.